Electron beam deflection device for use in connection with cathode-ray tubes of television receivers and the like



Feb, 18, I969 MITSUHARU AKATSU WITH CATHODE-RAY TUBES OF TELEVISION RECEIVERS AND THE LIKE Sheet l of 4 Filed April 2. 1965 336 E uni E cgswm QQ I B 9 336 5555b uggggbcu $53 58% 56x86 g EQmm gun EE Ski, m \Q B QwQ QEQ fiwxm 559% 65968 \m QEu Qm om om 6538 E 1 m \m QEb fifim m xmt mhc ma no cue m fl AW m E QQQ wt 'rnvEnToR mitsu a-m nkdtsu ATTORNEY 3, 1969 MITSUHARU AKATSU 3.

ELECTRON BEAM DEFLECTION DEVICE FOR USE IN CONNECTION WITH CATHODE-RAY TUBES OF TELEVISION V RECEIVERS AND THE LIKE Filed April 2. 1965 Sheet 2 of 4 F I6? 2 PRIOR ART DI C/ 3: 7 /6 M JY I L F/G 7 I Leff R/ghf (sfrefched) (shrunk) l I *"i In VENT OR m rtsiha 1 Katsu 1959 MITSUHARU AKATSU 3,423,353

ELECTRON BEAM DEFLECTION DEVICE FOR USE IN CONNECTION WITH CATHODE'RAY TUBES OF TELEVISION RECEIVERS AND THE LIKE Filed April 2, 1965 Sheet 3 of 4 FIG 8 :trwE nToR mi Lisa ha HKQIE BL (PM W. ewg q ATTORNEY 8. 1969 MITSUHARU AKATSUL 3, 2 3

ELECTRON BEAM DEFLECTION DEVICE FOR USE IN CONNECTION WITH CATHQDE'RAY TUBES OF TELEVISION RECEIVERS AND THE LIKE V Filed'April 2. 1965 Sheet 4' of 4 IHVE DTQR mVl'isu hdrq HKaBu Paupnal3 ATTORNEY United States Patent 3 428,853 ELECTRON BEAM DEFLECTION DEVICE FOR USE IN CONNECTION WITH CATHODE-RAY TUBES OF TELEVISION RECEIVERS AND THE LIKE Mitsuharu Akatsu, Yokohama, Japan, assignor to Hitachi, Ltd., Tokyo, Japan Filed Apr. 2, 1965, Ser. No. 445,222 Claims priority, appslication Japan, Apr. 4, 1964,

9/1s,902 U.S. (:1. 315-27 2 Claims Int. (:1. H01j 29/74 ABSTRACT OF THE DISCLOSURE This invention relates to an electron beam deflection device adapted for use in connection with a cathode-ray tube, especially, of television receivers.

In a deflection circuit of a television receiver the switching characteristic of transistors or vacuum tubes is generally utilized to el'rect desired deflection of the electron beam at a high efliciency. However, conventional television receivers have been defective in that distortion of the deflecting coil current in the horizontal deflection circuit tends to cause horizontal asymmetry of a picture on the screen of the caathode-ray tube. In an effort to eliminate the above-described defect, a circuit has been proposed to provide improved horizontal linearity of a picture on the screen of the cathode-ray tube.

The present invention intends to effect a further improvement in the circuit of this type and has for its object to provide an improved electron beam deflectioncircuit which is adapted for use with a cathode-ray tube and which is of the type utilizing the switching characteristic of a transistor or a vacuum tube to thereby minimize or completely eliminate any horizontally asymmetrical distortion of a televised picture due to resistances involved in the circuit.

According to the present invention, there is provided an electron beam deflection device for use in connection with a cathode-ray tube hav-in-g a deflecting coil energized by a current flowing therethrough to produce a magnetic field for deflecting the electron beam in said cathode-ray tube, means for supplying the current to said deflecting coil, and a switching element for periodically cutting off the current supplied to said deflecting coil, said device comprising means for causing the output voltage of said means for supplying the current to said deflecting coil to increase with the lapse of time during the conducting period of said switching element.

The above and other objects, advantages and particularities of the present invention will become obvious from the following description with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating the structure of a conventional television receiver;

FIG. 2 is a schematic diagram of a horizontal deflection circuit incorporated in the conventional television receiver of FIG. 1;

FIG. 3 is a graphic illustration of a current waveform 3,428,853 Patented Feb. 18, 1969 ICC I for the purpose of explaining the operation of the circuit of FIG. 2;

FIG. 4 is an explanatory view showing the manner of distortion of a televised picture when the horizontal deflection circuit of FIG. 2 is used;

FIG. 5 is a schematic diagram of a horizontal deflec t-ion circuit which is a priorly proposed improvement of the circuit of FIG. 2;

FIG. 6 is a graphic illustration of a current waveform for the purpose of'explaining the operation of the circuit of FIG. 5;

FIG. 7 is an explanatory view showing the manner of distortion of a televised picture when the horizontal deflection circuit of FIG. 5 is used;

FIG. 8 is a schematic diagram of a deflection circuit according to the present invention as it is embodied as a horizontal deflection circuit;

FIG. 9 is a graphic illustration of various current and voltage waveforms for the purpose of explaining the operation of the inventive circuit as shown in FIG. 8;

FIG. 10 is an explanatory view showing a distortionfree televised picture which is obtained when the circuit of the present invention is used;

FIG. 11 is a circuit diagram of another embodiment of the present invention;

FIG. 12 is a graphic illustration of current and voltage waveforms for the purpose of explaining the operation of the circuit of FIG. 11; and

FIG. 13 is a circuit diagram of still another embodiment of the present invention.

Before giving any detailed description with regard to the present invention, the structure of a conventional television receiver will first be described with reference to FIG. 1 so that the improvement effected by the present invention can more clearly be understood. In FIG. 1, reference numeral 1 designates an RF amplifier; 2, a frequency converter; 3, a local oscillator; 4, a video IF amplifier; 4', a video detector; 5, a video amplifier; 6, a cathode-ray tube (picture tube); 7, a sound IF amplifier; 8, a sound detector; 9, a sound power amplifier; 10, a speaker; 11, a synchronizing pulse separation and amplifying circuit; 12, a vertical oscillator; 13, a vertical deflection power amplifier; 14, a horizontal oscillation and AFC circuit; 15, a horizontal excitation transistor; 16, a horizontal power transistor; 17, a set of deflecting coils comprising a vertical deflecting coil D and a horizontal deflecting coil D 18, a fly-back transformer; and 19, a high-voltage rectifier tube. A portion surrounded by dotted lines and generally designated by reference numeral 20 indicates a horizontal deflection output circuit in the television receiver.

A typical example of the horizontal deflection output circuit 20 has a structure as shown in FIG. 2 and consideration will now be given to the circuit of FIG. 2. The transistor 16 in this circuit periodically repeats its conducting and cut-off states by being controlled by the output signals of the transistor 15. In a scanning period, the transistor 16 is driven to its conducting state and a substantially linearly increasing current flows through the horizontal deflecting coil D When the scanning period is terminated and a fly-back period begins, the transistor 16 is driven to its cut-off state and the current flowing through the horizontal deflecting coil D decreases abruptly. In a subsequent scanning period, the transistor 16 is again driven to its conducting state so that substantially linearly increasing current flows through the deflecting coil D and in a subsequent fly-back period, the transistor 16 is again driven to its cut-01f state so that the current flowing through the deflecting coil D is cut-off. By the repetition of such states, a saw tooth current necessary for the horizontal scanning can be obtained. The electron beam in the cathode-ray tube 6 is deflected by the magnetic field produced by this saw tooth current and thus the horizontal scanning necessary for the reproduction of pictures can be effected.

During the fly-back period, a pulse voltage called a flyback pulse appears across the deflecting coil D due to the abrupt decrease in the current. This fly-back pulse is boosted by the fly-back transformer 18 and then is rectified by the high-voltage rectifier tube 19. The high D.C. voltage thus obtained is used as a voltage for supply to the plate of the cathode-ray tube 6. The structure and operation of the horizontal deflection output circuit 20 as described above were already known in the art.

While this horizontal deflection output circuit 20 operates at a very high efficiency since it takes advantage of the switching characteristic of the horizontal power transistor 16, the deflecting coil D does not purely consist of the inductance L but necessarily includes a resistance r Further, each of the transistor 16 and a diode D has a slight resistance during its conducting period and the source of power supply also has its own internal resistance. Therefore, due to the influence exerted by these resistances, current I in the deflecting coil D can not have an ideal linear waveform as shown by dotted line in FIG. 3

but has a curvilinear waveform as shown by solid line therein.

Assume now that zero resistance is involved in the circuit, this deflecting coil current I can be expressed as I L t where E is a voltage of DC. power supply. Thus, the coil current I rectilinearly increases with time t and the current waveform as shown by dotted line in FIG. 3 can be obtained. When however the circuit includes resistances the sum of which is assumed to have a value r the deflecting coil current I in this case can be expressed as EB To E13 E1370 2 To -t 1 I r 1 e Ly Ly t t, since Ly Thus, the coil current I can no longer have a waveform which increases rectilinearly and its waveform departs from the straight line by an amount of the second member of the above equation, as shown by solid line in FIG. 3. This distortion in the deflecting coil current results in a distorted picture on the screen of the cathode-ray tube when, for example, the television signal is a signal representing the pattern of square meshes. That is, the distortion in the deflecting coil current results in a defective picture that the right-hand side half of the picture on the screen of the cathode-ray tube shrinks compared with the left-hand side of the picture.

The circuit as shown in FIG. 2 is further defective in that, in addition to the horizontally asymmetrical distortion in the televised picture due to resistances involved in the circuit, there appears a distortion of the nature that opposite edge portions of the picture are stretched compared with the central portion of the picture because the sensitivity of the deflecting coil is raised at portions corresponding to the opposite edges of the picture. It will be seen that two kinds of distortions as described above simultaneously appear in, the picture shown in FIG. 4. There is shown in FIG. 5 a circuit which is an improvement of the circuit of FIG. 2 and in which means is provided to improve the horizontal linearity of the picture.

The circuit as shown in FIG. 5 is substantially similar to the circuit of FIG. 2 but includes a capacitor C connected in series with the deflecting coil D to make it resonant with the inductance L of the deflecting coil D Thus the deflecting coil current I takes a waveform of S-like shape as shown in FIG. 6. The capacity of this capacitor C ranges from several pf. to several ten ,uf. whereas the inductance L of the deflecting coil D ranges from several hundreds ,uh. to several ten ,ull. When a television signal of square mesh pattern is used with the deflection circuit shown in FIG. 5, the picture is reproduced in a manner as shown in FIG. 7, in which it will be seen that the horizontally asymmetrical distortion still exists although the stretching at opposite edges of the picture is eliminated. Such horizontally asymmetrical distortion of the televised picture can be minimized or remedied by causing the DC. supply voltage E to increase With the time t as shown by E in FIG. 9. Since the capacitance value of the capacitor C is ordinarily of the order of several ,uf. to several ten uf., it is far easier to control the voltage across the capacitor C than to control the power source having such a high capacitance value of the order of several thousands uf.

The present invention is based on the finding as described above and will now be described in detail hereunder. An important feature of the present invention is that a pulse voltage is derived in synchronism with flyback pulses produced in a deflecting coil, this pulse voltage is conducted through a suitable impedance circuit to one terminal of a capacitor connected in series with the deflecting coil or to a portion corresponding to the power source for the deflecting coil, and the terminal voltage or the source voltage is controlled in a manner to increase with the lapse of time during the scanning period.

An embodiment of the present invention will first be described in detail with reference to FIG. 8, in which like reference numerals are used to designate like parts appearing in FIGS. 2 and 5. According to the present invention, a pulse voltage V having negative polarity as shown in FIG. 9 is derived at point X of FIG. 8. As shown in FIG. 9, this pulse voltage V has a polarity opposite to the polarity of a fly-back pulse voltage V (positive polarity) generated at point A of FIG. 8. The pulse voltage V thus derived is applied by way of a series circuit of an inductance L and a capacitor C to that terminal of a capacitor C which is disposed on the side of a deflecting coil D When now the pulse voltage V is applied to the series circuit of the capacitor C inductance L and capacitor C during the fly-back period, a current I as shown in FIG. 9 flows therethrough and a portion of electric charge stored in the capacitor C is transferred into the capacitor C through the inductance L so that the potential of the capacitor C is lowered. This corresponds to lowering of the source voltage for the deflecting coil D as shown by the voltage waveform E in FIG. 9. In the deflection circuit, any influence that may be exerted by the deflecting coil D during the fly-back period need not be taken into consideration because the deflecting coil D has an impedance sufficiently higher than that of the capacitor C In the subsequent scanning period, current having the waveform as shown by I in FIG. 9 flows from the capacitor C towards the capacitor C and the electric charge stored in the capacitor C gradually charges the capacitor C or the current is superposed on a deflecting coil current 1 This means that a voltage which increases with time t as shown by E in FIG. 9 is superposed on the source voltage E applied to the deflecting coil D and thus the horizontally asymmetrical distortion resulting from resistances involved in the circuit can be rendered almost negligible. It will be known that a perfectly square meshed picture free from any distortion as shown in FIG. 10 can be reproduced on the screen of the cathode-ray tube when the deflection circuit having such circuit arrangement is employed and a signal of square meshes is applied thereto.

Another embodiment of the present invention is shown in FIG. 11, in which it will be seen that a diode D is interposed in the inventive circuit as shown in FIG. 8 so that an increased amount of electric charge can be stored in the capacitor C during the fly-back period and the efliciency of the distortion correction can thereby be improved. In the circuit shown in FIG. 11, connection is made so that a pulse voltage V of negative polarity is produced at point X during the fiy-back period, that is, the pulse volta-ge V has its polarity reversed with respect to the polarity of a fly-baok pulse voltage V (positive polarity) produced at point A. During the fly-back period, the diode D conducts with the result that a current as shown by I in FIG. 12 flows from the capacitor C towards the capacitor C and a portion of electric charge stored in the capacitor C is rapidly transferred through the diode D into the capacitor C Therefore, the voltage drop across the capacitor C: as shown by a waveform V in FIG. 12 is caused during the fly-back period.

Then when the fly-back period is terminated and the scanning period begins, the potential V at point Y makes a rise to drive the diode D to its cut-off state and the electric charge stored in the capacitor C is gradually discharged through a choke coil L to charge the capacitor C As a result, the voltage across the capacitor C that is, voltage corresponding to the source voltage for the deflecting coil -D increases with the time and the horizontally asymmetrical distortion can thereby be minimized.

Still another embodiment of the present invention is illustrated in FIG. 13, in which an impedance or combined impedance circuit forming a passage for conducting a pulse voltage V of reverse polarity to the power source portion is generally indicated by reference character 2,,. Generally, a higher sensitivity and a higher eificiency of distortion correction can be obtained witli a smaller capacitance value of a capacitor C Also, the efficiency is higher at higher impedance values of a choke coil L connecting the capacitor C3 to the power source B in a DC. fashion, or of a deflecting coil D,,, and of inductance of the primary winding a fly-back transformer 18.

It will readily be understood that the invention described above is likewise effectively applicable to a case wherein a vacuum tube or the like is used as the switching element and to a case of a vertical deflection circuit.

From the foregoing description, it will be understood that, according to the invention, an electron beam deflection device of the type described can be formed solely by reactance elements having linear characteristics without any substantial loss and can be formed solely by passive circuit elements having stable and uniform characteristics which are readily available at low cost. The inventive deflection device having uniform characteristics can advantageously be used to provide a television picture quite free from distortion, improvement of which has been a matter of extreme difficulty in the prior art.

What is claimed is:

1. An electron beam deflection device for use in connection with a cathode-ray tube having'a deflecting coil energized by a current flowing therethrough to produce a magnetic field for deflecting the electron beam in said cathode-ray tube, a first capacitance for supplying the current to said deflecting coil, and a switching element for periodically cutting off the current supplied to said deflecting coil, said device comprising means for deriving a pulse voltage in synchronous relation with a fiy-back pulse generated in said deflecting coil during the cut-off period of said switching element, and an impedance circuit consisting of an inductance and a second capacitance for coupling said pulse voltage deriving means to said first capacitance, said device being operative in a manner that, during the cutoff period of said switching element, said pulse voltage is applied through said impedance circuit to said first capacitance to thereby transfer a portion of electric change in said first capacitance to said second capacitance, while during the conducting period of said switching element, the electric charge in said second capacitance is transferred through said inductance to said first capacitance whereby to cause the terminal voltage of said first capacitance to increase with the lapse of time during the conducting period of said switching element.

2. An electron beam deflection device for use in connection with a cathode-ray tube having a deflecting coil energized by acurrent flowing therethrough to produce a magnetic field for deflecting the electron beam in said cathode-ray tube, a first capacitance for supplying the current to said deflecting coil, and a switching element for periodically cutting off the current supplied to said deflecting coil, said device comprising means for deriving a pulse voltage in synchronous relation with a fly-back pulse generated in said deflecting coil during the cut-off period of said switching element, and an impedance circuit consisting of an inductance, a diode connected in parallel with said inductance and a second capacitance for coupling said pulse voltage deriving means to said first capacitance, said device being operative in a manner that, during the c-ut-ofi period of said switching element,

said pulse voltage is applied through said impedance circuitrto said first capacitance to thereby rapidly transfer a portion of electric change in said first capacitance to said second capacitance through said diode, 'while during the conducting period of said switching element, the electric charge in said second capacitance is slowly transferred through said inductance to said first capacitance whereby to cause the terminal voltage of said first capacitance to increase with the elapse of time during the conducting period of said switching element.

References Cited UNITED STATES PATENTS 3,349,279 10/1967 Sc-hafft 315 -27 RODNEY D. BENNETT, Primary Examiner.-

OHARLES L. WHITHAM, Assistant Examiner 

